A female Rimutaka Prison guard has been suspended after allegedly accepting cash to deliver a package to a prisoner.

Another two male guards have also been suspended in the past month for separate incidents in which they are alleged to have assaulted inmates.

It is understood the female guard backed out of the deal despite spending the cash, but her dealings were discovered by Corrections in January.

A prison source said the assault charges levelled at the other two guards were minor and involved dealing with confrontational prisoners who refused to follow orders and unit routines.

Even though the prisoners involved had not complained, the incident had been written up in a management report as being more serious than it was, resulting in the suspensions.

"It's been like that for years, that's why staff are hesitant to get involved because the first thing the management do is go to the prisoner and say: 'Do you want to lay an assault charge?' "

Rimutaka Prison human resources general manager Vince Arbuckle confirmed employment investigations into the three allegations were under way, but declined to comment on details.

The results could involve disciplinary action and a referral to police for consideration to lay charges, he said.

To improve the situation at Rimutaka, an "excellence plan" was being developed to help address the culture at the prison and improve staff performance.

New training would be introduced to improve staff safety, including skills in "de-escalation" and "tactical exiting".

There was zero tolerance to any form of violence or assault in prisons and appropriate action would be taken once the evidence had been assessed, he said.

"Integrity is vital for our staff, given the environment they work in and the need for them to uphold the law and act as role models for the offenders under our management."

Several breaches of protocol and assaults in the past few months have thrown the spotlight on Rimutaka.

In November, Corrections was forced to apologise to a woman visiting a prisoner after the pair were left locked in a non-contact meeting room for three hours when staff went home early and forgot about them.

The same month one guard resigned and another was suspended after they allowed a gang member to order pizza from his hospital bed.

Corrections chief executive Ray Smith told Parliament's law and order select committee that the November incidents were disappointing and said a deputy manager would be appointed to help support frontline staff.